(function (win, lib) {
	var doc = win.document;
	var docEl = doc.documentElement;
	var metaEl = doc.querySelector('meta[name="viewport"]');
	var flexibleEl = doc.querySelector('meta[name="flexible"]');
	var dpr = 0;
	var scale = 0;
	var tid;
	var flexible = lib.flexible || (lib.flexible = {});

	if (metaEl) {
		console.warn("将根据已有的meta标签来设置缩放比例");
		var match = metaEl
			.getAttribute("content")
			.match(/initial\-scale=([\d\.]+)/);
		if (match) {
			scale = parseFloat(match[1]);
			dpr = parseInt(1 / scale);
		}
	} else if (flexibleEl) {
		var content = flexibleEl.getAttribute("content");
		if (content) {
			var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
			var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
			if (initialDpr) {
				dpr = parseFloat(initialDpr[1]);
				scale = parseFloat((1 / dpr).toFixed(2));
			}
			if (maximumDpr) {
				dpr = parseFloat(maximumDpr[1]);
				scale = parseFloat((1 / dpr).toFixed(2));
			}
		}
	}

	if (!dpr && !scale) {
		var isAndroid = win.navigator.appVersion.match(/android/gi);
		var isIPhone = win.navigator.appVersion.match(/iphone/gi);
		var devicePixelRatio = win.devicePixelRatio;
		if (isIPhone) {
			// iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
			if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
				dpr = 3;
			} else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)) {
				dpr = 2;
			} else {
				dpr = 1;
			}
		} else {
			// 其他设备下，仍旧使用1倍的方案
			dpr = 1;
		}
		scale = 1 / dpr;
	}

	docEl.setAttribute("data-dpr", dpr);
	if (!metaEl) {
		metaEl = doc.createElement("meta");
		metaEl.setAttribute("name", "viewport");
		metaEl.setAttribute(
			"content",
			"initial-scale=" +
				scale +
				", maximum-scale=" +
				scale +
				", minimum-scale=" +
				scale +
				", user-scalable=no"
		);
		if (docEl.firstElementChild) {
			docEl.firstElementChild.appendChild(metaEl);
		} else {
			var wrap = doc.createElement("div");
			wrap.appendChild(metaEl);
			doc.write(wrap.innerHTML);
		}
	}

	function refreshRem() {
		var width = docEl.getBoundingClientRect().width;
		if (width / dpr > 540) {
			width = 540 * dpr;
		}
		var rem = width / 7.5;
		docEl.style.fontSize = rem + "px";

		// 纠错函数
		function adapt() {
			var d = window.document.createElement("div");
			d.style.width = "1rem";
			d.style.display = "none";
			var head = window.document.getElementsByTagName("head")[0];
			head.appendChild(d);
			var defaultFontSize = parseFloat(
				window.getComputedStyle(d, null).getPropertyValue("width")
			);
			return defaultFontSize;
		}
		rem = (rem * rem) / adapt();
		docEl.style.fontSize = rem + "px";

		flexible.rem = win.rem = rem;
	}

	win.addEventListener(
		"resize",
		function () {
			clearTimeout(tid);
			tid = setTimeout(refreshRem, 300);
		},
		false
	);
	win.addEventListener(
		"pageshow",
		function (e) {
			if (e.persisted) {
				clearTimeout(tid);
				tid = setTimeout(refreshRem, 300);
			}
		},
		false
	);

	if (doc.readyState === "compvare") {
		doc.body.style.fontSize = 12 * dpr + "px";
	} else {
		doc.addEventListener(
			"DOMContentLoaded",
			function (e) {
				doc.body.style.fontSize = 12 * dpr + "px";
			},
			false
		);
	}

	refreshRem();

	flexible.dpr = win.dpr = dpr;
	flexible.refreshRem = refreshRem;
	flexible.rem2px = function (d) {
		var val = parseFloat(d) * this.rem;
		if (typeof d === "string" && d.match(/rem$/)) {
			val += "px";
		}
		return val;
	};
	flexible.px2rem = function (d) {
		var val = parseFloat(d) / this.rem;
		if (typeof d === "string" && d.match(/px$/)) {
			val += "rem";
		}
		return val;
	};
})(window, window["lib"] || (window["lib"] = {}));
